Multi-packs collectively packing a plurality of to-be-packed objects, such as cans and bottles filled with drinking water or beer, are usually packed with a wrap around case K illustrated in FIG. 10. Further, the wrap around case K is brought into an assembled state, by performing folding and adhering on a blank, which is formed by performing-die cutting and scoring on a corrugated paperboard sheet.
FIG. 9 illustrates a blank B as a material to form a wrap around case K. This blank B includes two pairs of side panels 1 and 2 having different widthwise sizes which are alternately and continuously provided in a single direction with vertical fold lines “a” interposed therebetween, a joint tab panel 3 provided continuously on a side edge of a smaller-width side panel 1 positioned in one side with a vertical fold line “a” interposed therebetween, inner flaps 4 provided continuously on the respective opposite ends of the pair of smaller-width side panels 1 with lateral fold lines “b” interposed therebetween, and outer flaps 5 provided continuously on the respective opposite ends of the remaining pair of larger-width side panels 2 with lateral fold lines “b” interposed therebetween.
In assembling the wrap around case K using the blank B, one pair of side panels 1 and the remaining pair of side panels 2 are formed into a rectangular tubular shape as illustrated in FIG. 10 by folding them along the vertical fold lines “a”, then the joint tab panel 3 and a side panel 2 are adhered to each other at their portions to be overlapped with each other to form an angular tubular body 6. Thereafter, the inner flaps 4 and the outer flaps 5 are folded inwardly, and the inner flaps 4 and the outer flaps 5 are adhered to each other at their portions to be overlapped with each other to close the body 6 at its opposite-end openings. In the first step for closing a single opening of the body 6, a plurality of multi-packs P are housed inside the body 6. Reference numeral “7” denotes an adhesive agent for adhering the inner flaps 4 and the outer flaps 5 to each other at their portions to be overlapped with each other.
On the other hand, when a wrap around case K as described above is opened at home, in order to take out a necessary number of packed objects A such as beer cans therefrom and to store the remainder without increasing its volume, in many cases, the wrap around case K is opened at its end surface formed by the upper outer flaps 5 and the upper inner flaps 4 overlapped with each other, at a state where it is placed vertically. In this case, the outer flaps 5 in the outer side are stripped from the inner flaps 4 in the inner side, by putting the hands on the end edges of the outer flaps 5.
In this case, such a blank B is formed as follows. That is, as illustrated in FIG. 11A, a cutting die 22 is provided on a lower surface of an upper die 21 which can ascend and descend with respect to a cutting plate 20 made of stainless steel. Further, by descending the cutting die 22, as illustrated in FIG. 11B, die cutting is performed on a corrugated paperboard sheet S supported on the cutting plate 20, with a die-cutting blade 23 mounted in the lower surface of the cutting die 22. For performing such die cutting, a die-cutting blade with a straight-shaped cutting edge as described in Japanese Patent Laid-open Publication No. 2000-127258 or a die-cutting blade with a wavy cutting edge as described in Japanese Patent Laid-open Publication No. 2001-191297 has been generally employed.
However, the die-cutting blade described in Japanese Patent Laid-open Publication No. 2000-127258 has a cutting edge having a straight shape and, therefore, having higher acuteness. Further, the die-cutting blade described in Japanese Patent Laid-open Publication No. 2001-191297 is made to have a single wave shape with a larger radius of curvature since its edge portion has a wave shape, and its the cutting edge has relatively-higher acuteness. Accordingly, a blank B formed by die cutting therewith also has higher acuteness at its outer peripheral cut edges and, when the outer flaps 5 are stripped from the inner flaps 4 to open the wrap around case K by putting the hands on the end edges 5a of the outer flaps 5, the hands may be injured by touching the end edges 5a. Other end edges can also injure the hands, by being touched by the hands.
To cope therewith, in order to prevent injuries of the hands, Japanese Patent Laid-open Publication No. 2008-44664 proposes a corrugated paperboard box, wherein a reference line is defined in parallel with an end edge of an outer flap, there are provided, in a lattice shape, a plurality of fold lines orthogonal to the reference line, and a plurality of fold lines intersecting therewith and, further, there is formed a crushed portion in the corrugated paperboard having rigidity from an end edge thereof to a position spaced apart therefrom, in order to increase the softness of the corrugated paperboard box.
However, the aforementioned corrugated paperboard box includes the crushed portion spreading over a wide range and, therefore, may exhibit poor strength when being closed. Further, in order to form the fold lines therein, it is necessary to perform processing for forming slots for mounting a lattice-shaped pushing piece in the cutting die 22 illustrated in FIG. 11 and, also, it is necessary to perform processing for forming fitting slots in the cutting plate 20 at positions to face the lattice-shaped pushing piece, which induces the problems of an increase in the cost and a need for higher positioning accuracy in mounting the cutting plate 20 and the cutting die 22 in the die cutting machine.